The most common preparative HPLC columns have simply been tubes into which a packing medium is introduced and the bed allowed to settle by means of vibration and solvent flow. This method has been cumbersome and has had problems in the area of reproducibility. Other methods have been introduced to overcome these limitations but have their drawbacks. One method embodies radial compression in which the medium in a flexible tube is placed in a chamber and squeezed by pneumatic or hydraulic pressure. An obvious limitation to this method is the durability of the flexible tube, especially when in contact with various solvents used during the chromatographic process.
Other methods use some form of axial compression in which a a member acts on one end of the column bed to compress it. These methods have limitations in that the friction of the packing medium acting on the wall of the column causes somewhat of a compression gradient in the bed, thus resulting in a more tightly packed bed closest to the member end. Another limitation to this method has been pressure so that it is limited in use to only the larger particle size and less efficient packing medium.
It is the purpose of this invention to provide a column so structured as to insure reproducible bed regardless of the particle size of the medium used by nonuniformly decreasing the cross-section of the bed in the axial direction.
It is the further purpose of this invention to also compress the bed from one end in conjunction with decreasing the cross-section of the bed to maintain the bed efficiency over a long period of time and as the column is being used.